Various devices have been proposed to measure properties of tissues. For instance, U.S. Pat. No. 6,068,604 discloses a cartilage indentor instrument for measuring the compressive properties of cartilage. Other devices exist for harder tissue such as bone. For example, the Osteopenetrometer was designed for in vivo testing of trabecular bone during surgical procedures. That instrument was developed to characterize the mechanical properties of trabecular bone to obtain information relevant to reducing the problem of implant loosening following total knee arthroplasty. The Osteopenetrometer involved penetrations of lengths of over 8 millimeters and widths of over millimeters in diameter at implant sites during surgery.
More recently, devices have been proposed that utilize both a test probe and in most cases a reference probe for use in testing hard material such as bone tissue. Movement of the test probe relative to a reference probe is used to determine one or more parameters of the material being tested. Examples of these devices may be found, for instance, in U.S. Publication Patent Application No. 2007-0276292 and 2009-0093692 by common inventors of this application, and these applications are incorporated by reference. Devices such as those illustrated in the '292 and '692 Applications that use reference probes for some applications require a user to scrape away the periosteum, a technique requiring training, for in vivo use with a reference probe. Significant discussion of hardness and fracture measurements made with such instruments is found in the incorporated references.